The invention relates to a method of manufacturing a dielectric from a ferroelectric ceramic material having a perovskite structure with the basic formula ABO.sub.3. In the method, the dielectric is densely sintered in a reducing atmosphere at a temperature in the range from 1320.degree. to 1450.degree. C.
With the dielectric, multilayer capacitors, for example, can be manufactured. To manufacture multilayer capacitors, the ceramic material is densely sintered together with metal electrodes. Monolithic substrates can also be manufactured from the ceramic material, for example as discs or tubes. These components can be provided at their major surfaces with metal layers, for example electrode layers, either prior to or after sintering.
For cost considerations it is efficacious to use base metals or alloys of base metals for the electrodes. Such base metals may be, for example, nickel or chromium and alloys thereof.
In order to obtain particularly high capacitances, ferroelectric ceramic materials having perovskite structure are used as dielectrics. The dielectrics have the basic formula ABO.sub.3. In practice the A/B ratio is often chosen to deviate only slightly from 1, and several different ions are used both for the ions in the A-position and in the B-position in the perovskite-lattice. In order to be able to manufacture inexpensive capacitors with base metal electrodes, the ceramic material is densely sintered in a reducing atmosphere together with the electrode layers. This method relates in particular, to the production of multilayer capacitors.
Such dielectrics and multilayer capacitors manufactured therefrom with base metal electrodes are known from U.S. Pat. No. 3,920,781. In this patent, the A/B ratio lies within the range of from 0.95 to 1.00, and small quantities of the bivalent A-ions or of the quadrivalent B-ions are replaced by ions of a lower valency ("acceptor dopants"). The dielectrics are densely sintered in the temperature range from 1000.degree. C. to 1400.degree. C. in a reducing atmosphere having a partial oxygen pressure P.sub.O.sbsb.2 &lt;10.sup.-7 bar.
It has been found that the manufacture of these capacitors is particularly complicated with respect to maintaining the A/B-ratio in the desired range and preventing contamination by impurities. It has also been found that these capacitors do not exhibit optimum electrical properties in that the electric characteristic values thereof do not remain stable in life tests.